Exam 6: Chromosome Mutations: Variation in Number and Arrangement

Inversions suppress crossing over by providing a chemical imbalance because of breakpoints within certain genes.

In Drosophila melanogaster (2n = 8), a fly with seven chromosomes could be called a haplo -IV.

The condition known as cri -du -chat syndrome in humans has a genetic constitution designated as _.

Assume that an organism has a haploid chromosome number of 7. There would be 14 chromosomes in a monoploid individual of that species.

Translocations may be pericentric or paracentric.

Inversion heterokaryotypes are often characterized as having reduced crossing over and reduced fertility. Assume that you were examining a strain of organisms you knew to be inversion heterokaryotypes and saw a relatively high number of double chromatid bridges extending between anaphase I nuclei. What would be a likely explanation for this observation? Explain with a labeled diagram.

Fragile -X syndrome (or Martin -Bell syndrome) is the most common form of inherited mental retardation in humans. Is it more common in males or females? What is FMR1?

A deletion may set up a genetic circumstance where a recessive gene is expressed in an otherwise diploid organism.

What is meant by the terms acentric and dicentric?

What explanation is generally given for lethality of monosomic individuals?

Name the polyploid condition that is formed from the addition of one or more extra sets of chromosomes identical to the normal haploid complement of the same species.

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Although fertility is reduced in both sexes, Females have higher fertility rates than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3[2]:65-69) summarize data involving children born of Down syndrome Individuals. Assume that children are born to a female with Down syndrome and a normal 46 -chromosome male. What proportion of the offspring would be expected to have Down syndrome?

Describe the maternal age effect associated with Down syndrome.

Deletions are chromosomal aberrations in which some portion of a chromosome is missing. Describe a method using Drosophila deletions to determine the actual, physical location of a gene.

A genomic condition that may be responsible for some forms of fragile -X syndrome, as well as Huntington disease, involves _.

Under what circumstance can an individual with Down syndrome have 46 chromosomes?

In general, inversion and translocation heterozygotes are as fertile as organisms whose chromosomes are in the standard arrangement.

Inversions and translocations are without evolutionary significance.

An expected meiotic pairing configuration in a triploid would be a trivalent.

Familial Down syndrome is caused by a translocation involving chromosome 21.